1. Field of the Invention
This invention relates to dynamic dampers and a damping support apparatus using the dynamic dampers for a vehicle body such as a tractor body.
2. Description of the Related Art
A tractor has problems relating to vibrations such as engine vibration and running vibration. Such vibrations cause not only human body vibrations such as a whole body vibration and a local vibration (vibrations of hands and arms) of the driver, but malfunctioning and damage of various components.
As countermeasures against such vibrations, for example, a tractor cab is supported in independent suspension through rubber mounts, and dampermasses (mass members) provided for fenders or the like for varying (shifting) resonance points of vibration.
In the prior art, however, somewhat unsatisfactory results are obtained from the vibration absorption and shifting of resonance points in reducing vibration and booming noise. Further, the construction required for such an effort is complicated and costly.
The object of this invention, therefore, is to provide dynamic dampers and a damping support apparatus using the dynamic dampers for a vehicle body such as a tractor body, which are simple in construction, and yet are capable of reliably reducing vibration and booming noise.
The above object is fulfilled, according to this invention, by a dynamic damper comprising a cylindrical holder, a bar-shaped dampermass mounted in the holder so as to form a gap with an inner peripheral surface of the holder, and an elastomer disposed in at least part of the gap.
The above construction is simple, and yet is capable of not only shifting a resonance point of vibration with the mass of the bar-shaped dampermass, but reducing the transmission of vibration in a particular frequency range with the elastomer. Since the simple construction in which the bar-shaped dampermass is mounted in the cylindrical holder is provided, there is no need to employ a complicated construction for supporting the dampermass as seen in the prior art. That is, the dynamic damper according to this invention has a simple and inexpensive construction and assures a vibration damping effect.
In another aspect of this invention, the above object is fulfilled by a damping support apparatus for fixing an onboard structure such as a cab framework to a vehicle body, comprising support brackets attached to the vehicle body, cushion couplings each disposed between the onboard structure and one of the support brackets, and dynamic dampers each attached to one of the support brackets and adjacent one of the cushion couplings, each of the dynamic dampers including a cylindrical holder, mounting brackets formed on the holder and having connecting portions for connection to the support bracket, a bar-shaped dampermass mounted in the holder so as to form a gap with an inner peripheral surface of the holder, and an elastomer disposed in at least part of the gap.
The above damping support apparatus employs the dynamic dampers according to this invention having a number of advantages as noted hereinbefore. Thus, the apparatus reduces, effectively and at low cost, the driver""s fatigue and damage of various components due to vibration (and noise) of the vehicle body.
As a preferred embodiment of this invention, a construction is proposed in which the holder has caps attached to opposite ends thereof for restricting movement in longitudinal directions of the bar-shaped dampermass. The caps may be formed of an elastomeric material for elastically restricting movement in the longitudinal directions of the bar-shaped dampermass. With the caps formed of an elastomeric material, movement in the longitudinal directions of the bar-shaped dampermass is expected to reliably reduce the transmission of vibration in a particular frequency range. Furthermore, the caps may be constructed to seal the cylindrical holder. This will render the interior of the cylindrical holder waterproof to protect the bar-shaped dampermass from rain and mud.
As the elastomer for elastically supporting the bar-shaped dampermass, a plurality of O-rings may be mounted, as spaced from each other, peripherally of the bar-shaped dampermass. This construction provides an advantage in terms of cost. In this case, the bar-shaped dampermass may define circumferential grooves, with the O-rings mounted therein. This construction will prevent displacement of the O-rings, and facilitate assembly of dampermass to the cylindrical holder.
As a preferred arrangement of the dynamic dampers in the damping support apparatus, it is proposed to attach support brackets as cantilevers to the vehicle body, and place the dynamic dampers between the cushion couplings and free ends of the support brackets. An improved vibration damping effect is expected by arranging the dynamic campers adjacent the free ends of the support brackets.
Further, the support brackets may be box-shaped to contain the dynamic dampers therein, respectively. The support brackets then act as protective covers for the dynamic dampers.